E85?

[NinjaJack247]

My cousin and I were having a discussion about E85 the other day. The question came about "Can my/our protege 5's run on E85 or half and half?" I realize of course we can put it in and everything will seem alright, but in theory it's doing something horribly wrong to our engine. I would like to ask the guys on here what your thoughts are. Thanks

 

[larson701]

I doubt it. The ECU can compensate for the ethanol addition to a limited extent with the short term fuel trim, by adding between 20 and 25% additional fuel (this a limit within the ECU but may be an injector limitation). E85 requires a 30% addition. If E85 is run, I expect a CEL of some sort. I have run E30 with no issues and observed a SFT of around 10%. Also, not sure if there may be some material issues in the P5's fuel system for the addition ethanol. The P5 was designed and built prior to the push for higher ethanol fuels for high horsepower operation. Regardless, you will not be able to take advantage of the ethanol attributes since the ECU programming cannot be altered.

 

[P-Funk!]

Short answer - don't do it.

When converting to E85 you change the fuel pump, all seals and injectors. THEN you tune for E85.

So, not cost-effective by any stretch of the imagination.

 

[Ice88]

I doubt it. The ECU can compensate for the ethanol addition to a limited extent with the short term fuel trim, by adding between 20 and 25% additional fuel (this a limit within the ECU but may be an injector limitation). E85 requires a 30% addition. If E85 is run, I expect a CEL of some sort. I have run E30 with no issues and observed a SFT of around 10%. Also, not sure if there may be some material issues in the P5's fuel system for the addition ethanol. The P5 was designed and built prior to the push for higher ethanol fuels for high horsepower operation. Regardless, you will not be able to take advantage of the ethanol attributes since the ECU programming cannot be altered.

The ECU doesn't compensate for the additional ethanol.

To do this it'd require a flex fuel sensor, the protege5s do not have this. What it'd be compensating is based on the AFRs and Knock Detection.

Further, E85 does not require a 30% addition. That figure came about cause some numpty figured that because E85 at stoich is 30% richer that you need 30% more fuel. Which is just crap.

My cousin and I were having a discussion about E85 the other day. The question came about "Can my/our protege 5's run on E85 or half and half?" I realize of course we can put it in and everything will seem alright, but in theory it's doing something horribly wrong to our engine. I would like to ask the guys on here what your thoughts are. Thanks

Not without aftermarket ECU.

Would need larger injectors and if you wanted it to last a while a new fuel pump as well.

 

[kcbhiw]

We performed a fuel test on my CSP Miata with GRM and, on average, we discovered that we had to flow about 48% more fuel with E85 versus gasoline. I had to up-size the injectors to 550cc with a peak duty cycle of 55%. As a comparison, 93 octane pump gas had a peak duty cycle of 37% on the same injectors. The primary reason for this is that Ethanol simply does not have the same BTU content as gasoline (81,800 BTU/Gal vs. 114,500 BTU/Gal, respectively)

See the following article:
https://cobbtuning.zendesk.com/hc/en-us/articles/200178974-Fuel-Octane-Level-Testing

As others have said, you cannot simply get away with running E85 on a car that is not tuned for it. It'll run far too lean and power will suck.

 

[larson701]

The ECU doesn't compensate for the additional ethanol.

To do this it'd require a flex fuel sensor, the protege5s do not have this. What it'd be compensating is based on the AFRs and Knock Detection.

Further, E85 does not require a 30% addition. That figure came about cause some numpty figured that because E85 at stoich is 30% richer that you need 30% more fuel. Which is just crap.



Not without aftermarket ECU.

Would need larger injectors and if you wanted it to last a while a new fuel pump as well.

Actually, I agree. The fuel system is correcting flow based on the oxygen sensor. The numbers were stated to illustrate why a stock fuel system cannot compensate properly for E85. I have heard of people running up to E50 without a CEL but that does not mean the engine is operating optimally. Without tuning, which cannot be done on a stock Mazda ECU (am I wrong?), you cannot take advantage of the ethanol properties. Also note the need to reduce various components for compatibility with ethanol and the higher flow volumes as stated by others.

 

[kamesama980]

You can do it, but it'll suck.

not all FFVs have a flex fuel sensor. some (forget which) do just adjust via the O2 sensor along the lines of if it sees the fuel tank level rise by X amount or more, see if the O2 sensor readings change for the next 5 miles, if they do, figure the ethanol % changed and adjust. ^gross approximation but you get the idea.

Even flex-fuel vehicles are just adding fuel and spark advance (E85 also has a significantly higher octane rating). but even then, you lose out in the long run figuring cheaper fuel vs using more of it unless the price is a LOT less (like <2/3).

A dedicated E85 engine could balance it out by extracting more power from the less energy-rich fuel with very high compression and a lot of spark advance but at that point, you're talking built engine and aftermarket ECM...lots of money, a little more power maybe, with no economy improvement.